Process for the preparation of a thermoplastic polyurethane powder by precipitation polymerization using special catalysts

Abstract

The invention relates to a process for producing a thermoplastic polyurethane powder by precipitation polymerization, comprising the steps of: i. providing A) a solvent; B) at least one polyol with a molar mass between 60 g / mol and 250 g / mol; C) at least one diisocyanate; D) a catalyst, wherein the catalyst comprises or consists of a titanium, zinc, or zirconium transition metal complex or mixtures thereof; E) optionally a chain regulator E1) and / or an additive E2); ii. reacting the polyol B) with the diisocyanate C) in the solvent A) at a temperature of not more than 150 °C in the presence of the catalyst D), optionally the chain regulator E1) and / or the additive E2), to give the thermoplastic polyurethane, wherein the thermoplastic polyurethane precipitates as a solid in the solvent A) and forms a dispersion; iii.Separation from solvent A) and optional washing of the thermoplastic polyurethane with a solvent; and iv. drying of the thermoplastic polyurethane to the thermoplastic polyurethane powder; wherein the thermoplastic polyurethane powder has a mass mean of molar mass Mw of ≥ 50000 g / mol; an allophane content of ≤ 0.25 mol%, based on the total thermoplastic polyurethane powder; and a ratio of centrifuge mean of molar mass Mz to mass mean of molar mass Mw of ≤ 4.0, wherein the mass mean of molar mass Mw, the allophane content and the centrifuge mean of molar mass Mz are each determined by the methods set out in the description.

Description

[0001] The present invention relates to a process for producing a thermoplastic polyurethane powder by precipitation polymerization, the thermoplastic polyurethane powder obtained or obtainable by this process, and its use. Furthermore, the invention relates to a molded part obtained or obtainable by processing the thermoplastic polyurethane powder according to the invention. Finally, the invention also relates to the use of the catalyst according to the invention in a process for producing a thermoplastic polyurethane powder by precipitation polymerization, preferably in the process according to the invention. State of the art

[0002] The production of polymer powders is of great interest for use in powder sintering processes, as additives for structured surfaces, or as abrasives and lubricants in cosmetic applications and industry. Powder sintering processes are, in particular, methods in which a layer of powder is first applied, which is then sintered together or the powder particles are fused. Such processes are used, for example, for coating metals, polymers, wood, fibers, and other materials, where the surface is impregnated with powder by dipping in a fluidized bed, using a spray gun, or via dispersion, and then heated. In addition to epoxy and polyester resins, a wide variety of thermoplastic polymers such as polypropylene, polyamides, PVC, acrylates, and polyurethanes are also used for this purpose.

[0003] A process for the production of thermoplastic polyurethanes ("TPU") was already described in DE728981C in 1937. TPUs, among which an HDI-BDO adduct (HDI = 1,6-hexamethylene diisocyanate; BDO ​​= 1,4-butanediol) in particular was later marketed for a time under the names Perlon U, Igamid U, and Durethan U due to its combination of good properties such as high melting point, high modulus of elasticity, and good chemical resistance (O. Bayer, Angew. Chem. 1947, 59, 9, 257-288), are produced by reaction in a solvent (such as chlorobenzene and dioxane). The solvent is usually removed under vacuum. In some examples, the TPUs also precipitated as a gel or powder. However, it was later shown that the molecular chain lengths achieved were sometimes insufficient to obtain good polymer properties. Higher molecular weight TPU powders based on, for example, BDO-HDI are therefore not accessible.

[0004] However, most polymers, such as polypropylene, polyamide, or thermoplastic polyurethanes, which can be used, for example, for powder coatings or powder sintering processes, are produced in melt form. The polymer obtained in this way must then be brought into powder form in a further process step, for example, by milling. In the production of, for example, aliphatic thermoplastic polyurethanes in the melt, the pure monomers, such as 1,4-butanediol (BDO) and 1,6-hexamethylene diisocyanate (HDI), are reacted in a reactor to form an OH-terminated prepolymer. The second stage of the reaction is then carried out in a heavy-duty mixer by adding HDI (in a deficit; concentration factor approximately 0.98) to the prepolymer to produce the final product (BIOS Final Report No. 1472, ITEM No. 22, pp. 47-48).The disadvantages of this process include the high reaction temperature and the lengthy and inefficient mixing process, which leads to an increase in undesirable side reactions. This melting process can also be carried out in a modified form. In this case, the monomers BDO and HDI are converted to the prepolymer in a loop reactor or, alternatively, in static mixers (Fluitec reactors). In a second reaction step, this prepolymer reacts further with HDI in a reactive extrusion to form the final polymer. However, the disadvantages of a relatively high allophane content and the formation of gel particles cannot be avoided even when limiting the conversion (HDI under-concentration, concentration factor 0.98) (WO2021122279). In the melting processes described here as an example, the polymer is obtained in granular form after reactive extrusion and must be converted into powder form in a further process step.

[0005] For most polymers, such as polyamides (shown, for example, in EP3491066A1), polypropylene, and the also frequently used thermoplastic polyurethanes (see EP3512687B1), milling, especially cryogenic milling, is used to convert the granules into a powder. In cryogenic milling, the polymer granules are cooled to a very low temperature with liquid nitrogen and then milled. The desired particle size is separated from the milled material by sieving. The disadvantage of milling processes in general is that the particle shape is not spherical, but very irregular and angular. This negatively affects the flow behavior, and sieving the milled material is more complex. In addition, the particle size distribution is very broad during milling, so the yield is low, or the milling and sieving process has to be repeated several times.Furthermore, cryogenic milling is an expensive process due to the use of liquid nitrogen to adequately cool the polymers.

[0006] A special case is polyamide 12 (or polyamide 11), which is initially produced as PA 12 granules and dissolved under pressure in ethanol at elevated temperature. It is then precipitated and dried under very precisely controlled conditions (see, for example, EP0911142B1). The advantage of this method is that the polymer powder is obtained as relatively spherical particles with a particle size of < 100 µm (free-flowing) and does not require classification (sieving). Disadvantages of the process include the additional work steps and equipment, the associated costs, and the limited or no additives that can be added to the polymer.

[0007] The aforementioned processes are expensive due to their complexity and / or their disadvantages for the production of thermoplastic polyurethane powders with long chain lengths in combination with low allophane content and therefore limit the use of thermoplastic polyurethane powders or the processes dependent on them (powder sintering processes; filler for surface structuring) in industry.

[0008] Therefore, there is a need for a process for producing thermoplastic polyurethane powders with high molar masses and low allophane content. Object of the invention

[0009] The object of the present invention was therefore to provide a process for producing thermoplastic polyurethane powders with high molar masses and low allophane content. In particular, the process should lead to thermoplastic polyurethane powders with a mass mean molar mass of ≥ 50,000 g / mol and an allophane content of ≤ 0.25 mol%, based on the total thermoplastic polyurethane powder, as well as a ratio of centrifuge material (Mz) to mass mean (Mw) of ≤ 4.0. Furthermore, the process should ideally contain no highly toxic components and, at best, should not discolor the thermoplastic polyurethane powder obtained by the process, especially not yellow or yellowish. Finally, the process should preferably exhibit a more efficient and technically reliable reaction process.Furthermore, the thermoplastic polyurethane powders should be processed into molded parts which continue to have good or improved mechanical properties, in particular good elongation at break and a good modulus of elasticity. Solution to the problem and detailed description of the invention

[0010] The problem was solved by a process for producing a thermoplastic polyurethane powder by precipitation polymerization, comprising the following steps: i. Provision of A) a solvent; B) at least one polyol having a molar mass between 60 g / mol and 250 g / mol; C) at least one diisocyanate; D) a catalyst, wherein the catalyst comprises or consists of a titanium, zinc, or zirconium transition metal complex or mixtures thereof; E) optionally a chain regulator E1) and / or an additive E2); ii. Reaction of the polyol B) with the diisocyanate C) in the solvent A) at a temperature of not more than 150 °C in the presence of the catalyst D), optionally the chain regulator E1) and / or the additive E2), to the thermoplastic polyurethane, wherein the thermoplastic polyurethane precipitates as a solid in the solvent A) and forms a dispersion; iii. Separation from the solvent A) and optional washing of the thermoplastic polyurethane with a solvent; and iv. Drying of the thermoplastic polyurethane to the thermoplastic polyurethane powder; where the thermoplastic polyurethane powder a mass average of molar mass Mw of ≥ 50000 g / mol; an allophane content of ≤ 0.25 mol-%, based on the total thermoplastic polyurethane powder; and a ratio of centrifuge medium of molar mass Mz to mass average of molar mass Mw of ≤ 4.0; exhibits, wherein the mass mean of the molar mass Mw, the allophane content and the centrifugal mean of the molar mass Mz are each determined using the methods set out below.

[0011] In the course of the development work that led to the present invention, it was surprisingly discovered that the use of a special catalyst comprising or consisting of a titanium, zinc, or zirconium transition metal complex or mixtures thereof, results in thermoplastic polyurethane powders with high molar masses and low allophane content during precipitation polymerization. Furthermore, this process achieves a ratio of centrifuge medium (molar mass Mz) to mass medium (molar mass Mw) of ≤ 4.0. These catalysts according to the invention also have the advantage over conventionally used catalysts such as the organic tin-based catalyst DBTL (dibutyltin laureate) that they are not highly toxic, making them more environmentally friendly and preferable from both a health and regulatory perspective.

[0012] Furthermore, it was found that the use of the catalysts according to the invention leads to a more efficient reaction process in the precipitation polymerization. This increased efficiency is evident in the fact that the main precipitation of the thermoplastic polyurethane occurs significantly earlier (time savings equals higher throughput) and that the isocyanate concentration is kept as low as possible during the reaction and at the end of the isocyanate addition. An excessively high isocyanate concentration during the reaction and at the end of the isocyanate addition represents a considerable risk in industrial production due to the latent energy stored, in the event of a disruption, such as a cooling failure.

[0013] The number-mean molar mass (Mn), mass-mean molar mass (Mw), and centrifuge mean (Mz) of the thermoplastic polyurethane powder are determined by gel permeation chromatography (GPC). For this purpose, the sample to be measured is dissolved in a solution of 3 g potassium trifluoroacetate in 400 cubic centimeters of hexafluoroisopropanol (sample concentration approximately 2 mg / cubic centimeter). The respective GPCs are measured with the following components at a flow rate of 1 cubic centimeter / minute: Pump: HPLC pump 515 (Waters GmbH) Detector: Smartline RI detector 2300 (Knauer Wissenschaftliche Geräte GmbH) Columns: 1 guard column, 1000 × PSS PFG 7 µm, 300 × PSS PFG 7 µm, 100 × PSS PFG 7 µm in that order (PSS Polymer Standards Service GmbH) Degassing: PSS degasser (PSS Polymer Standards Service GmbH) Injection volume: 100 microliters Temperature: 23 °C - 25 °C Molar mass standard: Polymethyl methacrylate standard kit (PSS Polymer Standards Service GmbH)

[0014] The number mean of the molar mass (Mn or Mn) is the molar mass. M n ) is calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ n = ∑ i n i M i ∑ i n i in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol.

[0015] The mass mean of the molar mass (Mw or Mw). M w ) is also calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ w = ∑ i n i M i 2 ∑ i n i M i in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol.

[0016] The centrifuge medium of the molar mass (Mz or Mz) M z ) is calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ z = ∑ i n i M i 3 ∑ i n i M i 2 in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol.

[0017] The allophane content of the thermoplastic polyurethane powder is determined by 1H NMR. The measurement is performed with a Bruker AV III HD 600 spectrometer at 600 MHz in DMSO-D6 at 80 °C. The following peaks are evaluated: U= C H 2 -NH 2.98 ppm CH2 in urethane O= C H 2 -OH 3.43 ppm CH2 at OH groups N= N- H 6.6 ppm Urethane A= N- H 8.3-8.4 ppm Allophane

[0018] The allophanate concentration or allophanate content in mol% is calculated according to the following formula: Allophanat [mol-%] = 100 % * A / (A+N)

[0019] The key figure for revenue is derived from the formula: KZ = 1 / 1 + O / U

[0020] The solvent A) can be either a solvent mixture or a single solvent.

[0021] If the solvent mixture A) is a solvent mixture, the solvent mixture preferably comprises at least one first aprotic solvent A1) with a relative permittivity ε r of 2 to 20 and at least one second aprotic polar solvent A2) with a relative permittivity ε r of at least 24, wherein the relative permittivity ε r is measured at 20 °C and 100 kHz in each case.It is preferred that the first aprotic solvent A1) is halogenated aromatics, aromatics, ketones, ethers, esters and carbonates or mixtures thereof, in particular chlorobenzene and / or ortho-dichlorobenzene; cyclopentanone; cyclohexanone; heptan-4-one; amyl acetate; methoxypropyl acetate; xylene; benzene; toluene; ethylbenzene; cumene; acetophenone or mixtures thereof, more preferably chlorobenzene and / or the second aprotic polar solvent A2) is dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone, tetramethylurea (TMU), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidin ion, 1,3-dimethyl-2-imidazolidinone, X-ethyl-2-pyrrolidone, benzonitrile, dimethylacetamide; 1,2-propylene carbonate; ethylene carbonate; Gamma-butyrolactone or mixtures thereof, preferably dimethyl sulfoxide; 1,2-propylene carbonate; ethylene carbonate; gamma-butyrolactone comprises or consists thereof.

[0022] The ratio of the first aprotic solvent A1) to the second aprotic polar solvent A2) is preferably 300:1 to 1:9, more preferably 200:1 to 1:1, and even more preferably 100:1 to 8:2.

[0023] If solvent A) is a single solvent, it is preferred that solvent A) comprises or consists of chlorobenzene, ortho-dichlorobenzene; xylene; ethylbenzene; toluene; cumene; butyl acetate or amyl acetate, further preferably chlorobenzene.

[0024] Furthermore, it is preferred that the polyol B) comprises or consists of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol or mixtures thereof, wherein the polyol B) preferably contains at least 50.0 wt% 1,4-butanediol, particularly preferably at least 90.0 wt% 1,4-butanediol, based on the total weight of the polyol B).

[0025] The diisocyanate preferably comprises or consists of 1,4-butane diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, 1,1'-methylenebis(4-isocyanatocyclohexane), xylylene diisocyanate, in particular m-xylylene diisocyanate or mixtures thereof, wherein the diisocyanate C) further preferably contains at least 50.0 wt% 1,5-pentane diisocyanate or 1,6-hexane diisocyanate, based on the total weight of the diisocyanate C).

[0026] The catalyst comprises or consists of a titanium, zinc, or zirconium transition metal complex or mixtures thereof. It is preferred that the titanium, zinc, and / or zirconium transition metal complex comprises at least one multidentate ligand, and in particular that the zirconium transition metal complex comprises at least one multidentate ligand, wherein the multidentate ligand is more preferably at least one bidentate ligand, and even more preferably acetylacetone.It is particularly preferred that the catalyst D) is selected from the group comprising or consisting of tetraisopropyl orthotitanate, bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate, zirconium(IV) acetylacetonate or mixtures thereof, preferably bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate or mixtures thereof, particularly preferably bis(acetylacetonato)-titanium diisopropoxide. The catalyst bis(acetylacetonato)titanium diisopropoxide has the advantage of increasing the molar mass of thermoplastic polyurethane powders while simultaneously reducing the allophane content, and it exhibits little to no noticeable discoloration of the powder. Furthermore, compared to conventional catalysts such as DBTL, this catalyst is also more environmentally friendly and poses fewer health risks.For this reason, it is particularly preferred that the catalyst D) comprises or consists of bis(acetylacetonato)-titanium-diisopropoxide.

[0027] The optional chain regulator E1) may, for example, be selected from the group comprising or consisting of monofunctional zerewitinov H-acidic compounds, monofunctional isocyanates, or mixtures thereof. Examples of the optional chain regulator E1) include n-octanol, benzyl alcohol, n-octylamine, dioctylamine, □-caprolactam, propanone oxime, butane-1-thiol, acetylacetone, and diethyl malonate.

[0028] The optional additive E2) may, for example, be selected from the group comprising or consisting of stabilizers, dyes and markers or mixtures thereof.

[0029] Dyes are defined here as organic compounds that absorb at least part of the visible light spectrum between 380 nm and 790 nm. Dyes that are dissolved under the reaction conditions specified in step ii. and react with a Zerewitinow H-acidic compound or with an isocyanate group, and are thus covalently bonded to the thermoplastic polyurethane, are particularly preferred.

[0030] Markers, as used here, are compounds that are easily and specifically detectable using analytical methods. These can be, for example, aromatic compounds exhibiting specific UV absorption or UV absorption patterns, or which can be detected by fluorescence spectroscopy. Further examples of markers are isotopically enriched compounds that are readily detectable by NMR spectroscopy or by their radioactivity. Markers that are present in solution under the reaction conditions described in step ii and react with a Zerewitinow H-acidic compound or with an isocyanate group, thus forming a covalent bond with the thermoplastic polyurethane, are particularly preferred.

[0031] Furthermore, it is preferred that 30.0 to 95.0 parts by weight, preferably 60.0 to 90.0 parts by weight of solvent A); 2.0 to 40.0 parts by weight, preferably 3.0 to 20.0 parts by weight of polyol B); 3.0 to 40.0 parts by weight, preferably 5.0 to 25.0 parts by weight of diisocyanate C); 0.00001 to 5.0 parts by weight, preferably 0.0001 to 0.1 parts by weight of catalyst D); 0 to 10.0 parts by weight, preferably 0.001 to 1.5 parts by weight of chain regulator E1); and / or 0 to 20.0 parts by weight, preferably 0.0001 to 3.0 parts by weight of additive E2); are provided, each based on the total amount of solvent A), polyol B), diisocyanate C), catalyst D), chain regulator E1) and additive E2), which is normalized to 100 parts by weight.

[0032] The reaction in step ii. preferably takes place at a temperature of 50 °C to 150 °C, more preferably from 100 °C to 145 °C, and even more preferably from 120 °C to 140 °C, and / or at an isocyanate value of 0.95 to 1.1, more preferably from 0.97 to 1.02, and even more preferably from 0.98 to 1.0. The dispersion formed in step ii. preferably has a solids content of 5.0 to 50.0 wt.%, more preferably from 15.0 to 45.0 wt.%, and even more preferably from 20.0 to 40.0 wt.%, determined by gravimetric measurement with and without solvent.

[0033] The isocyanate number is calculated by dividing the molar amount of reactive isocyanate groups by the molar amount of reactive Zerewitino H-acidic groups. KZ = n Iso / n H − acid

[0034] The reaction in step ii. can also be carried out at a pressure lower or higher than the surrounding atmospheric pressure in the autoclave, for example, if solvent A1 and / or solvent A2 have a lower boiling point than the reaction temperature at approximately 1 bar. It is preferred to carry out the reaction in step ii. at ambient pressure.

[0035] Furthermore, it is preferred that the separation in step iii. is carried out by filtration, centrifugation, and / or evaporation of the solvents. The thermoplastic polyurethane can also be additionally washed with a solvent in step iii. Preferably, this solvent comprises or consists of a solvent with a boiling point between -30 °C and +250 °C (at 1 bar), preferably halogenated aromatics, aromatics and alkanes, ketones, ethers, esters, alcohols, nitriles, water, and carbonates or mixtures thereof, in particular chlorobenzene, methyl ethyl ketone, acetone, a C1-C6 alcohol and its esters, dimethyl carbonate, diethyl carbonate, or mixtures thereof, especially chlorobenzene.

[0036] The drying in step iv. is further preferably carried out by moving or mixing the drying material, particularly preferably in a paddle dryer.

[0037] It is also preferred that the thermoplastic polyurethane powder a bulk material with a molar mass Mw of 55,000 to 400,000 g / mol, more preferably of 60,000 to 300,000 g / mol, even more preferably of 65,000 to 200,000 g / mol, particularly preferably of 70,000 to 175,000 g / mol, most preferably of 750,000 to 150,000 g / mol; an allophane content of 0 to 0.20 mol%, more preferably of 0.001 to 0.15 mol%, particularly preferably of 0.01 to 0.10 mol%, based on the total thermoplastic polyurethane powder; and / or a ratio of centrifuge material with molar mass Mz to bulk material with molar mass Mw of ≤ 3.0, more preferably of 1.5 to 2.2 exhibits.

[0038] Depending on the choice of powder sintering process and application specifications for the polyurethane powder, powders with different grain sizes are used, but the grain sizes are usually in a range of up to 0.500 mm and smaller.

[0039] Another important aspect of particle size is the formation of the most stable dispersion possible during the reaction and for its processing. After scaling up to industrial levels, the dispersion must be transported by pumps, must not settle prematurely, and should also exhibit good filtration properties. If the particle size is too large, the particles settle too quickly, leading to deposits and increased wear on the pumps.

[0040] It is therefore preferred that the thermoplastic polyurethane powder contains ≥ 25.0 wt.% of a particle fraction of < 0.500 mm, based on the total thermoplastic polyurethane powder, more preferably 30.0 to 100 wt.%, and more preferably 40.0 to 80.0 wt.%. For the determination of the particle fraction, approximately 100 g of sample is sieved for 5 min using a Haver & Boecker laboratory sieve machine No. 7279 (manufactured in 1978) and the appropriate sieve set (e.g., 0.100 mm, 0.250 mm, 0.500 mm), and the individual fractions are then weighed.

[0041] The thermoplastic polyurethane according to step iii. and / or the thermoplastic polyurethane powder according to step iv. can / can further be impregnated with a stabilizer from a stabilizer solution. For this purpose, the thermoplastic polyurethane according to step iii. and / or the thermoplastic polyurethane powder according to step iv. is preferably dispersed in the stabilizer solution and then separated and dried. The stabilizer solution preferably comprises or consists of a solvent selected from the group comprising or consisting of solvents of the group consisting of chlorinated aromatics; aromatics; aliphatics; esters; ethers; alcohols; water; ketones; nitriles; carbonates; or mixtures thereof, or preferably the solvent(s) A1) from step i., wherein the solvent(s) preferably have a boiling point of < 250 °C at 1 bar; and a stabilizer dissolved therein, selected from the group comprising or consisting of sterically hindered phenol derivatives, organic phosphine, phosphite and / or phosphonate derivatives (generally also called phosphorus-based stabilizers), sulfur-containing antioxidants, 2,2,6,6-tetramethylpiperidine derivatives, benzotriazole derivatives, triazine derivatives, hydroxybenzophenone derivatives, cyanoacrylate derivatives, oxalinide derivatives or mixtures thereof; wherein the weight fraction of the stabilizer is preferably from 0.001 to 10.0 wt.%, more preferably from 0.05 to 5.0 wt.%, based on the total weight of the stabilizer solution.

[0042] Preferably, the stabilizer solution contains phosphorus(III) compounds as phosphorus-based stabilizers, which are oxidized to phosphorus(V) compounds upon heating in the presence of oxygen. Organic phosphites, phosphine compounds, and phosphonates, particularly organic phosphites and phosphonates, are also preferably used.

[0043] Particularly preferred is the phosphorus-based stabilizer selected from at least one compound according to the structures (1), (2), (3), (4), (5) and (6).

[0044] The compound (1) is classified as CAS: 31570-04-4 and is commercially available under the name Irgafos ™< 168 from BASF (Germany).

[0045] The compound (2) is classified as CAS: 237-249-1 and is commercially available under the name Brüggolen ™< H10 from the company Brüggeman (Germany).

[0046] The compound (3) is classified as CAS: 26741-53-7 and is commercially available under the name Irgafos ™< 126 from BASF (Germany).

[0047] Compound (4) is classified as CAS: 603-35-0 and is commercially available under the name Triphenylphosphine from BASF (Germany).

[0048] The compound (5) is classified as CAS: 80693-00-1 and is commercially available under the name ADK Stab ™< PEP 36 from Adeka (Japan).

[0049] The compound (6) is classified as CAS: 126050-54-2 and is commercially available under the name ADK Stab ™< HP-10 from Adeka (Japan).

[0050] Another suitable stabilizer containing phosphorus(III) is AddWorks™< LXR 568 MP from Clariant (Switzerland).

[0051] It is preferred that the phosphorus-based stabilizer is selected from the group comprising or consisting of compounds according to structures (1), (2), (4), (6) or mixtures thereof. The compound according to structure (1) and / or (2) is particularly preferred as the phosphorus-based stabilizer. These phosphorus-based stabilizers result in a particularly high tensile strength of the manufactured molded body.

[0052] The stabilizer solution may also contain a sterically hindered phenol. Mixtures of several such components and different stabilizers can also be used.

[0053] Preferably, the sterically hindered phenol is a compound of the general structure (7a) or (7b) where n means 1, 2, 3 or 4, R1, R2, and R3 each independently represent C1- to C4-alkyl or hydrogen. X represents a direct bond or an organic residue with C1- to C60, which may contain oxygen and / or nitrogen. R4 represents a direct bond, carbon, Ci-Cs alkyl, aryl, or a structure according to formula (8a), (8b), or (8c).

[0054] Particularly preferred is the sterically hindered phenol selected from at least one compound according to structures (9), (10), (11) and (12).

[0055] The compound (9) is classified as CAS: 6683-19-8 and is commercially available under the name ADK Stab ™< AO-60 from the company Adeka (Japan).

[0056] The compound (10) is classified as CAS: 85-60-9 and is commercially available under the name Songnox™< 4425 from Songwon Industrial Group (South Korea).

[0057] The compound (11) is classified as CAS: 23128-74 and is commercially available under the name Songnox™< 1098 from Songwon Industrial Group (South Korea).

[0058] The compound (12) is classified as CAS: 36443-68-2 and is commercially available under the name Irganox ™< 245 from BASF (Germany).

[0059] Furthermore, the stabilizer solution can optionally contain a sulfur-containing antioxidant. Mixtures of several such components can also be used.

[0060] A sulfur-containing antioxidant can, for example, have a structure according to R1-CH2-(S)x-CH2-R2, where x = 1 or 2 and where R1 and R2 can be the same or different and represent aromatic or aliphatic groups. Preferably, R1 and R2 are aliphatic groups, which can be linear or branched and can contain functional groups.

[0061] Examples of commercially available sulfur-containing antioxidants include dilauryl 3,3'-thiodipropionate (CAS 123-28-4), distearyl 3,3'-thiodipropionate (CAS 693-36-7), ditridecylthiodipropionate (CAS 10595-72-9); pentaerythritoltetrakis ([β-laurylthiopropionate (CAS 29598-76-3), 2,2'-thiodiethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (CAS 41484-35-9), dimyristylthiodipropionate (CAS 16545-54-3) and distearyl disulfide (CAS 2500-88-1), as well as mixtures of these substances.

[0062] Alternatively, the sulfur-containing antioxidant can also comprise one or more diphenyl thioesters such as 4,4'-thiobis(2-t-butyl-5-methylphenol) (CAS 96-69-5) and 2,2'-thiobis(6-t-butyl-4-methylphenol) (CAS 90-66-4).

[0063] Pentaerythritoltetrakis ([β-laurylthiopropionate] (CAS 29598-76-3) (structure (13)) is particularly preferred as a sulfur-containing antioxidant.

[0064] Furthermore, it is preferred that the thermoplastic polyurethane powder, after the aforementioned impregnation, contains 0.005 to 2.0 wt.% of the stabilizer from the stabilizer solution, based on the total weight of the thermoplastic polyurethane powder. The thermoplastic polyurethane powder obtained after impregnation preferably has a b-value of ≤ 4.0, more preferably of 0.1 to 2.5, determined in the CIE Lab color space using a spectrophotometer with illuminant D 65 at 8° according to DIN EN ISO 11664-4.Furthermore, it is preferred that the thermoplastic polyurethane powder exhibits a change in the b-value (Δb) after exposure to a temperature of 120 °C for a duration of 96 h and / or 155 °C for a duration of 6 h in each case under an air atmosphere of ≤ 3.5, preferably of 0.1 to 2.8, more preferably of 0.2 to 2.0, wherein the b-value in the CIE Lab color space is determined by means of a spectrophotometer with the illuminant D 65 at 8° according to DIN EN ISO 11664-4 and the change in the b-value is obtained by subtracting the b-value before the temperature exposure from the b-value after the temperature exposure.It was surprisingly found that the aforementioned impregnation according to the invention reduces the yellowing of the thermoplastic polyurethane powder, even after exposure to heat. This yellowing can otherwise be very pronounced in thermoplastic polyurethane powders produced by solvent processes, particularly aliphatic thermoplastic polyurethane powders, due to the drying step (German Plastics Practice, 1946, p. 304). The b-value in the CIE Lab color space, as described above, is used within the scope of the invention as a measure of the yellowing or the "whiteness" of the polyurethane powder. The CIE Lab color space consists of the L-value, the a-value, and the aforementioned b-value. "L" defines the lightness, "a" the red / green value, and "b" the yellow / blue value.To determine the b-value, a color measurement of the respective sample (approximately 3 mm powder layer between two coverslips for microscopy) is performed using a portable spectrophotometer (Konica Minolta CM5) with illuminant D 65 at 8° (observer angle) and diffuse illumination according to DIN EN ISO 11664-4. The powder's color is measured in reflectance and expressed in the CIE Lab color space using the L, a, and b values. The b-value is calculated from the measured spectral reflectance curve using the instrument's software.

[0065] Furthermore, the invention relates to a thermoplastic polyurethane powder obtained or obtainable according to the inventive method. As already explained above, these thermoplastic polyurethane powders have a high average molar mass in combination with a low allophanate content. If they have also been additionally impregnated according to the invention, they also exhibit less yellowing after exposure to temperature.

[0066] Furthermore, the invention relates to the use of the thermoplastic polyurethane powder according to the invention in an extrusion process, injection molding process, powder sintering process, solvent and / or melt process, in particular for the production of molded parts and / or coatings.

[0067] Furthermore, the invention relates to a molded part obtained or produced by processing the thermoplastic polyurethane powder according to the invention. Preferably, the molded part is free of gel particles. The gel particles are detected by a so-called gel determination. In this process, the thermoplastic polyurethane powder is injection-molded into a standard rod (dimensions 80 mm x 10 mm x 4 mm). The rod is placed with its flat side on a light table. The gel particles are visible to the naked eye in transmitted light as bright spots in the otherwise homogeneous sample. Additionally, the circular depressions on the smooth surface of the specimens, which are created by gel particles near the surface, are counted.To account for minor injection molding errors, if the total number of counted gel particles X < 5, the sample is considered free ("free of gel particles"), if 5 < X < 15, as slightly contaminated, 15 < X < 30 as heavily contaminated, and X > 30 as heavily contaminated.

[0068] Furthermore, the thermoplastic polyurethane powders, through further processing, preferably lead to molded parts which exhibit good or improved mechanical properties, in particular good elongation at break and a good modulus of elasticity. The mechanical properties, especially elongation at break and the modulus of elasticity / tensile modulus, are preferably determined by a tensile test based on the test method DIN EN ISO 527 using type 5A specimens (DIN EN ISO 527-2, 2 mm thick). The specimens are stored for at least 24 hours under standard conditions before the test. The tensile tests are carried out at 22 °C and 50% relative humidity using a Zwick Z010 universal testing machine at a speed of 10 mm / min. The modulus of elasticity is determined between 0.05% and 0.25% elongation using a secant test. The specimens can be, for example,This is produced by drying the thermoplastic polyurethane powder at 80 °C in a drying oven for 4 hours, then processing it on a microextruder (for example, MC 15 HT (15 mL) from Xplore) and bringing it into the required shape with the corresponding injection mold (for example, a Micro moulder IM 12).

[0069] Furthermore, the invention relates to the use of the catalyst according to the invention in a process for producing a thermoplastic polyurethane powder by precipitation polymerization, preferably in the process according to the invention, to increase the molecular weight Mw of the resulting or obtainable thermoplastic polyurethane powder. The molecular weight Mw is preferably determined as described above. The catalyst according to the invention is also described above and below.

[0070] Furthermore, the invention relates to the use of the catalyst according to the invention in a process for producing a thermoplastic polyurethane powder by precipitation polymerization, preferably in the process according to the invention, to improve the reaction progress of the precipitation polymerization. An improvement in the reaction progress preferably consists in the fact that the process is more efficient and technically more reliable, which is particularly evident in the fact that the main precipitation of the thermoplastic polyurethane occurs significantly earlier and / or the isocyanate concentration is as low as possible during the reaction process and at the end of the isocyanate addition. Types of embodiment:

[0071] The invention relates in particular to the following embodiments: According to a first embodiment, the invention relates to a process for producing a thermoplastic polyurethane powder by means of precipitation polymerization, comprising the steps: i. Provision of A) a solvent; B) at least one polyol having a molar mass between 60 g / mol and 250 g / mol; C) at least one diisocyanate; D) a catalyst, wherein the catalyst comprises or consists of a titanium, zinc, or zirconium transition metal complex or mixtures thereof; E) optionally a chain regulator E1) and / or an additive E2); ii. Reaction of the polyol B) with the diisocyanate C) in the solvent A) at a temperature of not more than 150 °C in the presence of the catalyst D), optionally the chain regulator E1) and / or the additive E2), to the thermoplastic polyurethane, wherein the thermoplastic polyurethane precipitates as a solid in the solvent A) and forms a dispersion; iii. Separation from the solvent A) and optional washing of the thermoplastic polyurethane with a solvent; and iv. Drying of the thermoplastic polyurethane to the thermoplastic polyurethane powder; where the thermoplastic polyurethane powder a mass average of molar mass Mw of ≥ 50000 g / mol; an allophane content of ≤ 0.25 mol-%, based on the total thermoplastic polyurethane powder; and a ratio of centrifuge medium of molar mass Mz to mass average of molar mass Mw of ≤ 4.0; exhibits, wherein the mass mean of the molar mass Mw, the allophanate content and the centrifugal mean of the molar mass Mz are each determined using the methods set out in the description.

[0072] According to a second embodiment, the invention relates to a method according to the first embodiment, characterized in that the solvent A) is a solvent mixture comprising at least a first aprotic solvent A1) with a relative permittivity ε r of 2 to 20 and at least a second aprotic polar solvent A2) with a relative permittivity ε r of at least 24, wherein the relative permittivity ε r is measured at 20 °C and 100 kHz in each case.

[0073] According to a third embodiment, the invention relates to a process according to the second embodiment, characterized in that the first aprotic solvent A1) is halogenated aromatics, aromatics, ketones, ethers, esters and carbonates or mixtures thereof, in particular chlorobenzene and / or ortho-dichlorobenzene; cyclopentanone, cyclohexanone; heptan-4-one; amyl acetate; methoxypropyl acetate; xylene; benzene; toluene; ethylbenzene; cumene; acetophenone or mixtures thereof, preferably chlorobenzene and / or the second aprotic polar solvent A2) is dimethyl sulfoxide, dimethylformamide, N -Methyl-2-pyrrolidone, tetramethylurea, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinion, 1,3-dimethyl-2-imidazolidinone, N -Ethyl-2-pyrrolidone, benzonitrile, dimethylacetamide, g-butyrolactone, ethylene carbonate, 1,2-propylene carbonate or mixtures thereof, preferably dimethyl sulfoxide; 1,2-propylene carbonate; ethylene carbonate; g-butyrolactone comprises or consists thereof.

[0074] According to a fourth embodiment, the invention relates to a method according to the second or third embodiment, characterized in that the ratio of the first aprotic solvent A1) to the second aprotic polar solvent A2) is 300:1 to 1:9, preferably 200:1 to 1:1, more preferably 100:1 to 8:2.

[0075] According to a fifth embodiment, the invention relates to a method according to the first embodiment, characterized in that the solvent A) comprises or consists of chlorobenzene, ortho-dichlorobenzene; xylene; ethylbenzene; toluene; cumene; butyl acetate or amyl acetate, preferably chlorobenzene.

[0076] According to a sixth embodiment, the invention relates to a process according to one of the preceding embodiments, characterized in that the polyol B) comprises or consists of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, or mixtures thereof, wherein the polyol B) preferably contains at least 50.0 wt.% 1,4-butanediol, particularly preferably at least 90.0 wt.% 1,4-butanediol, based on the total weight of the polyol B) and / or the diisocyanate C) comprises 1,4-butane diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, 1,1'-methylenebis(4-isocyanatocyclohexane), Xylylene diisocyanate, in particular m-xylylene diisocyanate or mixtures thereof, comprising or consisting of the diisocyanate C) preferably containing at least 50.0 wt% 1,5-pentane diisocyanate or 1,6-hexane diisocyanate, based on the total weight of the diisocyanate C).

[0077] According to a seventh embodiment, the invention relates to a process according to one of the preceding embodiments, characterized in that the reaction in step ii. takes place at a temperature of 50 °C to 150 °C, preferably from 100 °C to 145 °C, more preferably from 120 °C to 140 °C and / or at an isocyanate number of 0.95 to 1.1, preferably 0.97 to 1.02, more preferably 0.98 to 1.0.

[0078] According to an eighth embodiment, the invention relates to a method according to one of the preceding embodiments, characterized in that the dispersion formed in step ii. has a solids content of 5.0 to 50.0 wt.%, preferably 15.0 to 45.0 wt.%, more preferably 20.0 to 40.0 wt.%, determined by gravimetric measurement with and without solvent.

[0079] According to a ninth embodiment, the invention relates to a method according to one of the preceding embodiments, characterized in that the thermoplastic polyurethane powder a bulk material with a molar mass Mw of 55,000 to 400,000 g / mol, preferably of 60,000 to 300,000 g / mol, more preferably of 65,000 to 200,000 g / mol, particularly preferably of 70,000 to 175,000 g / mol, most preferably of 75,000 to 150,000 g / mol; an allophane content of 0 to 0.20 mol%, preferably of 0.001 to 0.15 mol%, particularly preferably of 0.01 to 0.10 mol%, based on the total thermoplastic polyurethane powder; and / or a ratio of centrifuge material with molar mass Mz to bulk material with molar mass Mw of ≤ 3.5, preferably of 1.9 to 2.8; exhibits.

[0080] According to a tenth embodiment, the invention relates to a method according to one of the preceding embodiments, characterized in that the titanium, zinc and / or zirconium transition metal complex comprises at least one multidentate ligand, in particular at least the zirconium transition metal complex comprises at least one multidentate ligand, wherein the multidentate ligand is preferably at least one bidentate ligand, more preferably acetylacetone.

[0081] According to an eleventh embodiment, the invention relates to a process according to one of the preceding embodiments, characterized in that the catalyst D) is selected from the group comprising or consisting of tetraisopropyl orthotitanate, bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate, zirconium(IV) acetylacetonate or mixtures thereof, preferably bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate or mixtures thereof, particularly preferably bis(acetylacetonato)-titanium diisopropoxide.

[0082] According to a twelfth embodiment, the invention relates to a thermoplastic polyurethane powder obtained or obtainable by a method according to one of embodiments 1 to 11.

[0083] According to a thirteenth embodiment, the invention relates to the use of a thermoplastic polyurethane powder according to the twelfth embodiment in an extrusion process, injection molding process, powder sintering process, solvent and / or melt process, in particular for the production of molded parts and / or coatings.

[0084] According to a fourteenth embodiment, the invention relates to a molded part obtained or obtainable by processing a thermoplastic polyurethane powder according to the twelfth embodiment.

[0085] According to a fifteenth embodiment, the invention relates to the use of a catalyst as defined in one of embodiments 1, 10 or 11 in a process for producing a thermoplastic polyurethane powder by precipitation polymerization, preferably in a process according to one of embodiments 1 to 11, to increase the molecular weight Mw of the thermoplastic polyurethane powder obtained or obtainable. Examples

[0086] The present invention will be explained in more detail with reference to the following examples. Measurement methods:

[0087] The following measurement methods were used: GPC method for determining number mean of molar mass Mn, mass mean of molar mass Mw and centrifuge mean of molar mass Mz:

[0088] Determination by gel permeation chromatography (GPC). For this purpose, the sample to be measured was dissolved in a solution of 3 g potassium trifluoroacetate in 400 cubic centimeters of hexafluoroisopropanol (sample concentration approx. 2 mg / cubic centimeter). The respective GPCs were measured with the following components at a flow rate of 1 cubic centimeter / minute: Pump: HPLC pump 515 (Waters GmbH); Detector: Smartline RI detector 2300 (Knauer Wissenschaftliche Geräte GmbH); Columns: 1 guard column, 1000 × PSS PFG 7 µm, 300 × PSS PFG 7 µm, 100 × PSS; PFG 7 µm in this order (PSS Polymer Standards Service GmbH); Degassing: PSS degasser (PSS Polymer Standards Service GmbH); Injection volume: 100 microliters; Temperature: 23 °C - 25 °C; Molar mass standard: Polymethyl methacrylate standard kit (PSS Polymer Standards Service GmbH).

[0089] The number mean of the molar mass ( M n) was calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ n = ∑ i n i M i ∑ i n i in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol.

[0090] The mass average of the molar mass ( M w ) was also calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ w = ∑ i n i M i 2 ∑ i n i M i in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol.

[0091] The centrifuge medium of the molar mass ( M z) was calculated from the data obtained by measuring gel permeation chromatography using the following equation: M ¯ z = ∑ i n i M i 3 ∑ i n i M i 2 in g / mol where: M i the molar mass of the polymers of the fraction i is, so that M i < M i +1 for everyone i, in g / mol ni the amount of substance of the polymer of the fraction i, in mol. Allophane content:

[0092] The allophane content was determined by 1H NMR. The measurements were performed with a Bruker AV III HD 600 spectrometer at 600 MHz in DMSO-D6 at 80 °C.

[0093] The following peaks were evaluated: U=C H 2 -NH 2.98 ppm CH2 in urethane O=C H 2 -OH 3.43 ppm CH2 at OH groups N=N- H 6.6 ppm Urethane A= N- H 8.3-8.4 ppm Allophane

[0094] The aliphatic allophanate concentration in mol% was calculated using the following formula: Allophanat mol − % = 100 % * A / A + N

[0095] The key figure for revenue is derived from the formula: KZ = 1 / 1 + O / U Isocyanate titration:

[0096] By back titration of dibutylamine with 0.1 N hydrochloric acid after addition of an excess of amine to an isocyanate solution using a Metrohm, 751 GPD titrino 685 Dosimat and 728 stirrer. Materials:

[0097] The following materials were used for components A) to E): Solvent A):

[0098] Chlorobenzene (alone or in the mixture as the first aprotic solvent A1)) of analytical grade, obtained from Azelis Deutschland GmbH, relative permittivity: □ r = 5.6 (see Reference 1 below) Dimethyl sulfoxide (DMSO) 99.9% (in the mixture as the second aprotic polar solvent A2)), obtained from Merck, relative permittivity: ε r = 47.3 (see Reference 2 below)

[0099] References: 1.) DK Handbook, Endress+Hauser Messtechnik GmbH&Co. (1999); 2.) Hunger et al J. Chem. Eng. Data 2010, 55, 5, 2055-2065. Polyol B :

[0100] 1,4-Butanediol (BDO) (Company: Ashland), Purity: ≥ 99% wt.%, Diisocyanate C):

[0101] 1,6-Hexamethylene diisocyanate (HDI) (Company: Covestro AG), Purity: ≥ 99% wt.%; Catalyst D):

[0102] Titanium tetraisopropoxide (or tetraisopropyl orthotitanate; Ti(OiPr)₄) sourced from Sigma-Aldrich, purity: ≥ 97 wt.%; Bis(acetylacetonato)-titanium(IV) oxide (TiO(acac)₂) sourced from Sigma-Aldrich, purity: ≥ 95 wt.%; Bis(acetylacetonato)-titanium diisopropoxide (Ti(OiPr)₂(acac)₂) sourced from Sigma-Aldrich, purity: ≥ 75 wt.% in isopropanol; Zirconium(IV) acetylacetonate (Zr(acac)₄) sourced from Sigma-Aldrich, purity: ≥ 97 wt.%; zinc(II) acetate (Zn(OAc)₂) sourced from Sigma-Aldrich, purity: ≥ 99 wt.%; zinc(II) acetylacetonate (Zn(acac)₂) sourced from Sigma-Aldrich, purity: ≥ 95 wt.% Other catalysts:

[0103] Dibutyltin laureate (DBTL) sourced from Sigma-Aldrich, purity: ≥ 95 wt.%; 1,4-Diazabicyclo[2.2.2]octane (DABCO) sourced from Sigma-Aldrich, purity: ≥ 99 wt.%. Chain regulator E1):

[0104] n-Octanol of analytical grade, sourced from Arcos Organics, purity: ≥ 99% wt.%. Experimental procedure and results: Experiment series 1: Comparison of different catalysts in a solvent mixture

[0105] 1000 mL of chlorobenzene, 50 mL of DMSO, 201.8 g (2.24 mol) of BDO, 2.86 g (22 mmol) of n-octanol, optionally 40 mg of catalyst, and 189.8 g (1.13 mol) of HDI were placed in a 2 L reaction vessel equipped with a thermometer, reflux condenser, and mechanical stirrer. The mixture was separated, covered with nitrogen, and heated to reflux on an oil bath (the reaction started at approximately 90 °C and heated the mixture). A further 189.8 g (1.13 mol) of HDI was then added rapidly using a dropping funnel while stirring, maintaining reflux. After the HDI addition was complete, the mixture was heated to reflux for another 5 h. During this time, the thermoplastic polyurethane precipitated as a white powder. The residual isocyanate content was measured, neutralized with butanol, and the dispersion was cooled while stirring. The powder was filtered off and the residue on the Büchner funnel was washed once with 250 mL of chlorobenzene.The filter cake was then suspended in 250 mL of chlorobenzene, stirred at room temperature for 30 min, and filtered. This process was repeated a total of 6 times. The filter cake was then dried under vacuum at 120 °C.

[0106] The results are summarized in Table 1: Table 1 Attempt catalyst Mw [g / mol] Mz / Mw Allophane content [mol%] Further 1a no 64114 1.8 0.1 Not according to the invention 1b DBTL 70870 1.9 - * Not according to the invention 1c Ti (OiPr) 4 156210 2.6 <0.1 Product yellow 1d TiO(acac) 2 108503 1.9 <0.1 Product slightly yellowish 1e Zr(acac) 4 80815 1.9 <0.1 1f DABCO 49809 1.9 0.1 Not according to the invention 1g Zn(OAc) 2 94454 2.5 0.1 1h Zn(acac) 2 117748 2.7 0.1 1i Ti(OiPr) 2 (acac) 2 113882 2.1 - * * - = no allophanate detectable.

[0107] The experiments according to the invention clearly show that the use of catalysts according to the invention, i.e., the titanium, zinc, and zirconium transition metal complexes, increases the molar mass of the thermoplastic polyurethane powders obtained or producible by precipitation polymerization, while still achieving low allophane content and Mz / Mw ratios. In particular, titanium- and zinc-based catalysts (experiments 1c, 1d, 1e, 1g, 1h, and 1i) prove to be very effective with regard to increasing the molar mass. A good balance between effective molar mass increase and simultaneous non-discoloration of the thermoplastic polyurethane powder was achieved especially by the bidendate titanium catalyst titanium(IV)-bis(acetylacetonato)-di-(isopropylate) from experiment 1i, which combines an increase in molar mass Mw with low allophane generation and minimal discoloration of the product.

[0108] In comparison, it is shown that conventional catalysts such as the amine-based catalyst DABCO do not increase the molar mass. Although the known organic tin-based catalyst DBTL also increases the molar masses compared to experiment 1a, where no catalyst is used, this catalyst is highly toxic and, compared to experiments 1c, 1d, 1e, 1g, 1h and 1i according to the invention, still performs worse with regard to increasing the molar mass of the thermoplastic polyurethane powder. Experiment series 2: Use of catalysts in a solvent

[0109] 1200 mL of chlorobenzene, 139.7 g (0.775 mol) of BDO, 130.45 g (1.10 mol) of HDI, and optionally 15 mg of titanium(IV)-bis(acetylacetonato)-di-(isopropylate) were placed in a 2 L reaction vessel equipped with a thermometer, reflux condenser, and mechanical stirrer at room temperature. The mixture was then heated on an oil bath until reflux occurred. 130.45 g (0.775 mol) of HDI was then rapidly added using a dropping funnel while stirring, allowing the mixture to boil at reflux. After the HDI addition was complete, the mixture was heated at reflux for a further 5 h. The solution was tested for residual isocyanate content and cooled to room temperature with continuous stirring. The thermoplastic polyurethane precipitated as a white powder. The mixture was cooled, filtered (using a Nuckese filter), and the residue was washed twice with 150 mL of chlorobenzene and twice with 150 mL of acetone. The white solid was dried in a convection oven at approximately 80 °C for 24 hours.

[0110] The results are summarized in Table 2: Table 2 Attempt catalyst Mw [g / mol] Mz / Mw Allophane content [mol%] 2a no 36771 1,9 - * 2b Ti(OiPr) 2 (acac) 2 105948 2,2 < 0,1 * - = no allophanate detectable.

[0111] It is shown that even when using only one solvent, the molar mass can be significantly increased with a simultaneously low allophane content and Mz / Mw ratio when a catalyst according to the invention (see experiment 2b compared to 2a) is used. Experiment series 3: Reaction process

[0112] 1200 mL of chlorobenzene, 136.1 g (1.51 mol) of BDO, and 0.39 g (3 mmol) of n-octanol (and optionally 3 mg of the catalyst titanium(IV)-bis(acetylacetonato)-di-(isopropylate)) were placed in a 2 L reaction vessel equipped with a thermometer, reflux condenser, and mechanical stirrer. The mixture was then heated on an oil bath until reflux (approximately 132 °C). Next, 257.5 g (1.53 mol) of HDI were added using a dropping funnel while stirring. evenlyHDI was added over an hour. During the addition (and for 30 minutes afterward), a sample was taken every 10 minutes, the amount of HDI added was recorded, and the isocyanate content was determined. After the HDI addition was complete, the solution was heated under reflux for a further 12 hours. The isocyanate content was determined after approximately 5 hours. Finally, the solution was tested for residual isocyanate, the isocyanate was neutralized with butanol, and the dispersion was cooled to room temperature with continuous stirring. The mixture was filtered, and the residue was washed three times with 200 mL of chlorobenzene. The white solid was dried in a convection oven at approximately 80 °C for 24 hours.

[0113] The results are summarized in Tables 3 (without catalyst) and 4 (with catalyst). Table 3 Time [min] Isocyanate content titrated [%] Isocyanate content calculated [%] Amount of HDI added [%] Amount of isocyanate conversion [%] Residual amount of isocyanate [%] Start HDI bonus 0 0 0 0 0 0 10 0,19 1,26 16,6 14 2,6 20 0,61 2,52 33,2 25 8,2 30 0,94 3,8 48,6 27 21,6 40 1,52 5,05 65,2 46 19,2 Start of felling 50 1,71 6,3 81,8 59 22,8 End HDI bonus 60 2,06 7,6 100 73 27 Heavy precipitation 70 0,9 7,6 100 88 12 411 0,23 7,6 100 97 3 880 0,2 7,6 100 97,4 2,6 Table 4 Time [min] Isocyanate content titrated [%] Isocyanate content calculated [%] Amount of HDI added [%] Amount of isocyanate conversion [%] Residual amount of isocyanate [%] Start HDI bonus 0 0 0 0 0 0 10 0,08 1,26 16,6 15,5 1,1 20 0,1 2,52 33,2 29,5 3,7 30 0,16 3,8 48,6 46,5 2,1 40 0,08 5,05 65,2 64,2 1 Heavy precipitation 50 0,36 6,3 81,8 77,1 4,7 End HDI bonus 60 - * 7,6 100 - * - * 73 0,72 7,6 100 90,5 9,5 86 0,57 7,6 100 92,5 7,5 93 0,59 7,6 100 92 8 106 0,49 7,6 100 93,5 6,5 415 0,32 7,6 100 96 4 810 0,28 7,6 100 96,3 3,7 * Sampling was not possible at this time because the solution was still boiling too strongly due to precipitation.

[0114] Overall, the reaction pathways of the uncatalyzed and catalyzed reactions were similar. The polymer precipitation occurred at approximately the same HDI conversion, and the final isocyanate concentrations were also comparable.

[0115] Significant differences were observed in the precipitation time of the thermoplastic polyurethane with regard to the amount of HDI added and the isocyanate concentration during HDI dosing. In the case of the uncatalyzed reaction, the main precipitation occurred approximately 10 minutes after the complete addition of HDI, while in the catalyzed reaction, the main precipitation of the thermoplastic polyurethane was observed about 10 minutes before the end of HDI addition. The isocyanate concentration in the reaction solution of the uncatalyzed synthesis reached its highest value of approximately 2 wt% at the end of HDI addition, which corresponds to about 27% unused isocyanate. This represents over a quarter of the total reaction energy as latent energy and thus a considerable risk in industrial production in the event of a disruption, e.g., in the cooling system.

[0116] In contrast, no isocyanate concentration exceeding 1 wt% was measured during the entire reaction in the catalyzed reaction. The highest amount of free isocyanate was also determined at the end of the HDI addition in the catalyzed reaction and amounted to less than 10% of the total isocyanate used. Thus, in the catalyzed reaction, the highest measured amount of isocyanate, also at the end of the HDI addition, was only about one-third of that measured in the non-catalyzed reaction.

Claims

1. A process for the production of a thermoplastic polyurethane powder by precipitation polymerization, comprising the steps of: i. providing A) a solvent; B) at least one polyol having a molar mass between 60 g / mol and 250 g / mol; C) at least one diisocyanate; D) a catalyst, wherein the catalyst comprises or consists of a titanium, zinc, or zirconium transition metal complex or mixtures thereof; E) optionally a chain regulator E1) and / or an additive E2); ii. reacting the polyol B) with the diisocyanate C) in the solvent A) at a temperature of not more than 150 °C in the presence of the catalyst D), optionally the chain regulator E1) and / or the additive E2), to give the thermoplastic polyurethane, wherein the thermoplastic polyurethane precipitates as a solid in the solvent A) and forms a dispersion; iii.Separation from solvent A) and optional washing of the thermoplastic polyurethane with a solvent; and iv. drying of the thermoplastic polyurethane to the thermoplastic polyurethane powder; wherein the thermoplastic polyurethane powder has: • a mass mean of molar mass Mw of ≥ 50000 g / mol; • an allophane content of ≤ 0.25 mol%, based on the total thermoplastic polyurethane powder; and • a ratio of centrifuge mean of molar mass Mz to mass mean of molar mass Mw of ≤ 4.0; wherein the mass mean of molar mass Mw, the allophane content and the centrifuge mean of molar mass Mz are each determined by the methods set out in the description.

2. Method according to claim 1, characterized by the fact that the solvent A) is a solvent mixture comprising at least one first aprotic solvent A1) with a relative permittivity ε rfrom 2 to 20 and at least one second aprotic polar solvent A2) with a relative permittivity ε r of at least 24, where the relative permittivity ε r Each measurement is taken at 20 °C and 100 kHz.

3. Method according to claim 2, characterized by the fact thatthe first aprotic solvent A1) halogenated aromatics, aromatics, ketones, ethers, esters and carbonates or mixtures thereof, in particular chlorobenzene and / or ortho-dichlorobenzene; cyclopentanone, cyclohexanone; heptan-4-one; amyl acetate; methoxypropyl acetate; xylene; benzene; toluene; ethylbenzene; cumene; Acetophenone or mixtures thereof, preferably chlorobenzene and / or the second aprotic polar solvent A2) dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone, tetramethylurea, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinion, 1,3-dimethyl-2-imidazolidinone, N-ethyl-2-pyrrolidone, benzonitrile, dimethylacetamide, g-butyrolactone, ethylene carbonate, 1,2-propylene carbonate or mixtures thereof, preferably dimethyl sulfoxide; 1,2-propylene carbonate; ethylene carbonate; g-butyrolactone comprises or consists thereof.

4. Method according to claim 2 or 3, characterized by the fact thatthe ratio of the first aprotic solvent A1) to the second aprotic polar solvent A2) is 300:1 to 1:9, preferably 200:1 to 1:1, more preferably 100:1 to 8:

2.

5. Method according to claim 1, characterized by the fact that the solvent A) comprises or consists of chlorobenzene, ortho-dichlorobenzene; xylene; ethylbenzene; toluene; cumene; butyl acetate or amyl acetate, preferably chlorobenzene.

6. Method according to any of the foregoing claims, characterized by the fact thatthe polyol B) comprises or consists of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol or mixtures thereof, wherein the polyol B) preferably contains at least 50.0 wt% 1,4-butanediol, particularly preferably at least 90.0 wt% 1,4-butanediol, based on the total weight of the polyol B) and / or the diisocyanate C) comprises or consists of 1,4-butane diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, 1,1'-methylenebis(4-isocyanatocyclohexane), xylylene diisocyanate, in particular m-xylylene diisocyanate or mixtures thereof, wherein the Diisocyanate C) preferably contains at least 50.0 wt% 1,5-pentane diisocyanate or 1,6-hexane diisocyanate, based on the total weight of diisocyanate C).

7. Method according to any of the foregoing claims, characterized by the fact thatthe reaction in step ii. is carried out at a temperature of 50 °C to 150 °C, preferably from 100 °C to 145 °C, more preferably from 120 °C to 140 °C and / or at an isocyanate number of 0.95 to 1.1, preferably 0.97 to 1.02, more preferably 0.98 to 1.

0.

8. Method according to any of the foregoing claims, characterized by the fact that The dispersion formed in step ii. has a solids content of 5.0 to 50.0 wt.%, preferably 15.0 to 45.0 wt.%, more preferably 20.0 to 40.0 wt.%, determined by gravimetric measurement with and without solvent.

9. Method according to any of the foregoing claims, characterized by the fact thatthe thermoplastic polyurethane powder • a bulk material with a molar mass Mw of 55,000 to 400,000 g / mol, preferably of 60,000 to 300,000 g / mol, more preferably of 65,000 to 200,000 g / mol, particularly preferably of 70,000 to 175,000 g / mol, most preferably of 75,000 to 150,000 g / mol; • an allophane content of 0 to 0.20 mol%, preferably of 0.001 to 0.15 mol%, particularly preferably of 0.01 to 0.10 mol%, based on the total thermoplastic polyurethane powder; and / or • a ratio of centrifuge material with molar mass Mz to bulk material with molar mass Mw of ≤ 3.5, preferably of 1.9 to 2.

8.

10. Method according to any of the foregoing claims, characterized by the fact that the titanium, zinc and / or zirconium transition metal complex comprises at least one multidentate ligand, wherein the multidentate ligand is preferably at least one bidentate ligand, more preferably acetylacetone.

11. Method according to any of the foregoing claims, characterized by the fact thatthe catalyst D) is selected from the group comprising or consisting of tetraisopropyl orthotitanate, bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate, zirconium(IV) acetylacetonate or mixtures thereof, preferably bis(acetylacetonato)-titanium(IV) oxide, bis(acetylacetonato)-titanium diisopropoxide, zinc(II) acetate, zinc(II) acetylacetonate or mixtures thereof, particularly preferably bis(acetylacetonato)-titanium diisopropoxide.

12. Thermoplastic polyurethane powder, obtained or obtainable by a process according to any one of claims 1 to 11.

13. Use of a thermoplastic polyurethane powder according to claim 12 in an extrusion process, injection molding process, powder sintering process, solvent and / or melt process, in particular for the production of molded parts and / or coatings.

14. Molded part obtained or obtainable by processing a thermoplastic polyurethane powder according to claim 12.

15. Use of a catalyst as defined in any one of claims 1, 10 or 11 in a process for producing a thermoplastic polyurethane powder by precipitation polymerization, preferably in a process according to any one of claims 1 to 11, to increase the molecular weight Mw of the thermoplastic polyurethane powder obtained or obtainable.

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